A vertical metal oxide semiconductor (MOS) transistor with parallel RESURF trenches in the drain drift region has chamfered corners to reduce stress on the portions of the vertical MOS transistor nears corners of the substrate. The parallel RESURF trenches are surrounded by a RESURF termination trench. The vertical MOS transistor experiences premature breakdown and breakdown instability due to uncontrolled regions of the substrate inside the termination trench at the chamfers.